In the conventional railway load supporting system the load is pivotally carried on spaced wheel trucks at load support centers so that when the train negotiates a curve the trucks pivot relative to the load at the support centers. When extremely long loads, such as large electrical transformers and bridge beams, are transported by rail, the load is supported adjacent each of its ends between relatively widely separated sets of running gear. While such an arrangement is satisfactory under normal straight running conditions, when the load must negotiate a relatively sharp curve the load swings inboard for such a distance that it will either strike a wayside obstacle or it will be unable to negotiate the curve.
Various schemes have been proposed in the prior art for overcoming the problem outlined above of enabling long and wide loads to negotiate curves without striking roadside obstacles. It has, for example, been suggested that removable pins can be inserted through the supporting beams and into the running gear at points inboard of the support centers to cause the load to swing around pivot centers separated by a lesser distance than are the load support centers.
Another arrangement which has been proposed is to provide a surface on the running gear bolster to which the load is applied and which permits sliding or rolling movement between the member carrying the load and the bolster surface. In such an arrangement, there is provided a rigid beam connecting the member applying the load to a pin or the like at the point on the bolster inboard of the load point at which it is desired to have the load pivot.
In yet another arrangement, described in my prior patent, U.S. Pat. No. 3,837,295, each end of the load is supported on a bolster carried by the running gear by means of an arcuate sliding connection comprising a transversely extending arcuate way and an arcuate slide disposed in the way and connected to the load so as to constrain the load to swing about a pivot point which is the center of the arc of movement of the sliding connection. While this last arrangement has been successful, it has the disadvantage of requiring an independent lateral shifting device in order to clear certain obstacles.
Further, all of these "reduced pivot" arrangements, as they are often called, suffer the drawback that the effective pivot center is either fixed or is adjustable only by stopping the train and performing a suitable manual operation such as inserting pivot pins. Thus for a nonstop run, the pivot center is effectively fixed. Since the selection of a pivot center involves a compromise between competing considerations of clearance and car stability, operation on atypical track portions will be less than optimum. For example, if the car assembly is operating on a track portion with a rapidly changing curvature, the rapid lateral shifting of the load support center due to the reduced pivot may result in overloading of the outside wheels. Under such conditions, uniformity of axle load becomes more important than clearance.